The manufacture of various articles e.g., chairs, backrests, cushions, and seats, frequently involves the use of adhesives to join or bond different materials to one another. Adhesives are selected based upon manufacturing and material processing limitations, as well as end product performance requirements. Accordingly, adhesive packages are derived from many different chemical families. U.S. Pat. No. 5,259,656, for example, discloses a hot melt film adhesive which is a high molecular weight polyalkylene adipate polyester that is stated to be useful in a thermoplastic adhesive applications. Additionally, U.S. Pat. No. 5,068,143 discloses the production and use of thermoformable materials composed of a thermoplastic polyesterurethane, as described in greater detail hereafter.
Seat manufacturing in the transportation sector typically includes the attachment of a trim cover to a seat cushion, the trim cover providing a decorative effect. Synthetic materials like vinyl, natural materials such as leather, and fabrics that are knitted or woven represent common trim cover materials. Seat cushions are normally composed of polyurethane foam or elastomeric fibers.
Various production manufacturing methods are used to attach trim covers to seat cushions. Economics and expertise usually drive the selection of the best available option. U.S. Pat. No. 4,692,199, assigned to Lear Corporation, discloses a manufacturing process that uses a steam-based system to attach a trim cover to a seat cushion, notably an automotive seat cushion. In the process disclosed in the '199 patent, a thermoplastic adhesive is disposed between a trim cover and a seat cushion. This assembly is then heated by superheated steam to the softening temperature of the adhesive (i.e., above 95.degree. C. (200.degree. F.)) which enables the wetting of both trim and cushion materials by adhesive. Subsequently, the assembly is cooled below the softening temperature of the adhesive which causes the adhesive to solidify, creating a durable attachment or bond between the trim cover and the seat cushion. Thermoplastic adhesives such as those disclosed in U.S. Pat. No. 4,692,199 require a relatively high temperature to be maintained for an appreciable period for the adhesive to soften and wet the substrates to be bonded.
A thermoplastic adhesive of the thermoplastic polyurethane (TPU) type is illustrated by U.S. Pat. No. 5,068,143, where a high molecular weight polyester diol with a molecular weight in the range of 1200-10,000 Da (Daltons) is reacted with a diisocyanate at an isocyanate index of from 75 to 110, preferably 90. The thermoplastic polyesterurethane may be cast as a soft film and after heating, provides increased open times which are useful during shoe manufacturing. The long open time of the hot-melt adhesive before the polymer crystallizes eliminates multiple reheating. However, high temperature film strength is inadequate for many applications.
Thermoset adhesives have also been used for trim cover applications. The viscosity of many thermosetting polymer systems is low, and therefore penetration, wetting and adhesion to a foam substrate and trim cover or other substrates are, in general, not problematic. However, thermoset systems are generally slow to cure, and thus fabrication time is sharply increased. Increasing catalyst levels in one and two component adhesives can decrease cure time. However, ultimate physical properties of the adhesive are often compromised. Moreover, unless the catalyst is of the latent type, pot life of the adhesive will be shortened dramatically. Many types of thermosetting adhesives cannot be supplied in the form of films.
Each of these known adhesive systems and/or their application present process limitations making desirable the need for an improved adhesive package.